Manganese is a chemical element with the element symbol Mn and of the atomic number 25. It is in the 7th subgroup, the manganese group, on the periodic table. Manganese is a silvery-white, hard, very brittle transition metal that in some ways resembles iron in its properties. It naturally occurs primarily as brownstone and is mined in large quantities. 90 percent of the mined manganese is used in the steel industry in the form of ferromanganese as an alloying component of steel. In this process, it removes oxygen and sulfur from the steel and at the same time improves through-hardening. Manganese (IV) oxide, which is used as a cathode in alkaline manganese batteries, is also important in economy. As a component of various enzymes, the element is of high biological importance. It acts in a central point in the photosynthesis cycle, where a manganese-calcium cluster is responsible for the oxidation of water to oxygen.